Carbon sources as factors affecting the secondary metabolism of the maize pathogen Fusarium verticillioides

Label-free Raman microspectroscopic imaging with chemometrics for cellular investigation of apple ring rot and nondestructive early recognition using near-infrared reflection spectroscopy with machine learning

Apple ring rot caused by Botryosphaeria dothidea can cause fruit decay during the growth and storage stages of apple fruit. Understanding the infection process and cellular defense response at the cellular micro-level holds immense importance in the field of prevention and control. Consequently, there is a pressing need to develop suitable chemical imaging analysis methods. Here we proposed a label-free, high-throughput imaging method for cellular investigation of apple fruit ring rot infected by Botryosphaeria dothidea, based on confocal Raman microspectroscopic imaging technology combined with multivariate curve resolution-alternating least squares algorithm (MCR-ALS). We conducted Raman measurements on every apple fruit and obtain an image cube. This cube was then unfolded into an augmented matrix in a column-wise manner. We proceeded with simultaneous MCR-ALS analysis, resolving the single-substance spectrum and concentration profile from the mixed signals. Lastly, the accurate and pure molecular imaging of low methoxyl pectin, high methoxyl pectin, cellulose, lignin, and phenols were realized by refolding the resolved concentration data to construct the composition image. Thereafter, we realized the study of the spatial-temporal changes distribution of the above substances in the cuticle and cell wall of green and red apples at different stages of infection. The imaging method proposed in this paper is expected to provide a chemical imaging strategy for studying pathogen infection process and fruit defense response at the cellular level. In addition, by utilizing a fiber-optic probe near-infrared reflection spectrometer in conjunction with machine learning, we developed a rapid and non-destructive classification method. This method allows for the timely identification of apples exhibiting early infection by Botryosphaeria dothidea. Notably, both principal component analysis-quadratic discriminant analysis and support vector machine achieved a classification accuracy of 100%.

Influence of Carbon Sources on the Phenolic Compound Production by Euglena gracilis Using an Untargeted Metabolomic Approach

Industrial development and urbanization has led to the diverse presence of metals in wastewater that are often improperly treated. The microalgae Euglena gracilis can tolerate high concentrations of metal via the excretion of organic metabolites, including phenolics. This study aims to evaluate how carbon amendment stimulates phenolic compound production by E. gracilis. The number, relative intensity and molecular composition of the phenolic compounds were significantly different between each of four carbon amended cultures (i.e., glutamic acid, malic acid, glucose, reduced glutathione) during the log phase. Phenolic compounds were mainly produced during the minimum growth rate, likely a response to stressful conditions. A better understanding of phenolic compounds production by E. gracilis and the impact of growth conditions will help identify conditions that favor certain phenolic compounds for dietary and metal chelation applications.

Effect of Carbon Sources on the Production of Volatile Organic Compounds by Fusarium verticillioides

The aim of the present study was to evaluate the effect of different carbon sources on the hydrocarbon-like volatile organic compounds (VOCs) of Fusarium verticillioides strain 7600 through a Principal Component Analysis approach, and to explore their diesel potential by using data from the literature. The fungus was cultivated in GYAM culture medium, and five carbon sources were evaluated: glucose, sucrose, xylose, lactose, and fructose. The VOCs were collected using a close-loop apparatus and identified through GC-MS. The same profile of 81 VOCs was detected with all treatments, but with different relative percentages among carbon sources. The production of branched-chain alkanes (30 compounds) ranged from 25.80% to 38.64%, straight-chain alkanes (12 compounds) from 22.04% to 24.18%, benzene derivatives (12 compounds) from 7.48% to 35.58%, and the biosynthesis of branched-chain alcohols (11 compounds) was from 6.82% to 16.71%, with lower values for the remaining groups of VOCs. Our results show that F. verticillioides has the metabolic potential to synthesize diesel-like VOCs. Further research should include the optimization of culture conditions other than carbon sources to increase the production of certain groups of VOCs.

Carbon sources to enhance the biosynthesis of useful secondary metabolites in Fusarium verticillioides submerged cultures

Fusarium verticillioides is a prolific producer of useful secondary metabolites such as naphthoquinone pigments, monoterpenes, and sesquiterpenes, as well as the harmful mycotoxins fumonisins. A strategy to increase their production includes creating a proper nutritional environment that enables the fungus to produce the compounds of interest. The aim of the present work was to study the effect of different carbon sources (glucose, fructose, xylose, sucrose, and lactose) on secondary metabolites biosynthesis in F. verticillioides submerged cultures. The production of volatile terpenes was evaluated through gas chromatography coupled to mass spectrometry. The quantification and identification of pigments was conducted using a UV/VIS spectrophotometer and NMR spectrometer, respectively. The quantification of fumonisin B₁ and fumonisin B₂ was performed by high-performance liquid chromatography. Our results showed that the biosynthesis of naphthoquinone pigments, monoterpenes, and sesquiterpenes was highest in cultures with fructose (13.00 ± 0.71 mmol/g), lactose [564.52 × 10^-11 ± 11.50 × 10^-11 μg/g dry weight (DW)], and xylose (54.41 × 10^-11 ± 1.55 × 10^-11 μg/g DW), respectively, with fumonisin being absent or present in trace amounts in the presence of these carbon sources. The highest biosynthesis of fumonisins occurred in sucrose-containing medium (fumonisin B₁: 7.85 × 10³ ± 0.25 × 10³ μg/g DW and fumonisin B₂: 0.38 × 10³ ± 0.03 × 10³ μg/g DW). These results are encouraging since we were able to enhance the production of useful fungal metabolites without co-production with harmful mycotoxins by controlling the carbon source provided in the culture medium.

Structural and metabolic performance of p-cresol producing microbiota in different carbon sources

p-Cresol (PC) is a potential off-flavor and carcinogenic compound that affects food flavor and safety. However, controlling the production of PC when making fermented food is hindered by a lack of knowledge of the microbial diversity and the growth requirements of the microbiota that produce PC. To address this, the present study used three media with selected carbon sources (glucose, ethanol and lactic acid) to explore the microbial origin of PC and to determine the preferred carbon source for the PC-producing microbiota in the pit mud of the strong-aroma type Baijiu. The results showed that the different carbon sources affected the microbial structure, especially of the PC-producing microbiota. Glucose led to the highest production of PC and lactic acid to the lowest. The production of PC was significantly correlated (p < 0.05, |ρ| > 0.6) with Dorea, Sporanaerobacter, Tepidimicrobium, Tissierella Soehngenia, Clostridium and Sedimentibacter in the glucose medium; with Proteiniborus, Ruminococcus and Sporanaerobacter in the ethanol medium; and with Lutispora and Tepidimicrobium in the lactic acid medium. Multiphasic metabolite target analysis further indicated that the PC-producing microbiota could also metabolize flavor compounds. Lactic acid could inhibit the production of PC and ensure that the microbiota produced the appropriate flavor compounds during culture. Collectively, Dorea, Sporanaerobacter, Tepidimicrobium, Tissierella_Soehngenia, Clostridium, Sedimentibacter, Proteiniborus, Ruminococcus and Lutispora were identified as potential PC producers in three media with glucose preferred as the carbon source. These findings provide a perspective on the microbiota and carbon source preference for ultimately improving the quality of distilled alcoholic beverage.